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You need to model the 2-12 response period as maintenance of working memory. Additionally, you might want to modulate the maintenance period by load. You are right that the signal overlaps, but the neural activity doesn't; so, the events should be separable. Just make sure you model everything. If you are still concerned, you could create 3 separate events for the 2 second delay periods and ignore them. Best Regards, Donald McLaren ================= D.G. McLaren, Ph.D. Postdoctoral Research Fellow, GRECC, Bedford VA Research Fellow, Department of Neurology, Massachusetts General Hospital and Harvard Medical School Office: (773) 406-2464 ===================== This e-mail contains CONFIDENTIAL INFORMATION which may contain PROTECTED HEALTHCARE INFORMATION and may also be LEGALLY PRIVILEGED and which is intended only for the use of the individual or entity named above. If the reader of the e-mail is not the intended recipient or the employee or agent responsible for delivering it to the intended recipient, you are hereby notified that you are in possession of confidential and privileged information. Any unauthorized use, disclosure, copying or the taking of any action in reliance on the contents of this information is strictly prohibited and may be unlawful. If you have received this e-mail unintentionally, please immediately notify the sender via telephone at (773) 406-2464 or email. On Wed, Dec 8, 2010 at 9:07 AM, Andres Roman <[log in to unmask]> wrote: > Hi, > > I have been following the discussion about jittered trial design and had a > couple of questions related to my design. I am analyzing data from 4 groups > of a delayed response task. The task consist of two runs (32 trials by run) > with 6 different loads of stimulus. The trials start with a fixed 4 sec > period were the stimulus is shown (series of letters) followed by a > variable > delay of 2 to 12 seconds, following this there is a fixed period of 1.5 > secs > were the subject is supposed to match and answer according to to the series > of letters that were shown at the start of the trial, finishing the trial > with an ITI of variable duration (3-5) seconds. I am able to to model both > the start of the trial quite well and the response section of 1.5 sec. I am > using a duration of 1 second and a parametric modulator that uses the load > effect for the 4 sec section. In the case of the response section I used a > duration of 1.5 (length of the whole answer period) and the same parametric > modulator used before (load). My problem is that I am afraid that since the > jittered minimum interval is 2 secs the signal in those trials overlaps > between each other. Is there a way to model this variable jitter interval > in > a way that could maximize my signal? A proposed contrast to model the > jitter > interval? Or exclude the jittered trials that have a value of less than 4 > seconds? > > Thank you very much for any ideas to deal with this. > -- > Andres Roman-Urrestarazu >